The calendering of tubular knitted fabric is a finishing operation which is performed during the end stage of the processing cycle, and which has the purpose of drafting the tubular fabric, in general by means of a steaming and flattening between heated cylinders, after previously expanding and overfeeding it.
Such an operation allows the width of the tubular knitted fabric to be brought back to the required value, by determining the dimensions thereof, and allows the same tubular fabric to be given a commercially acceptable appearance and touch.
Normally, expander devices for the tubular knitted fabric are used, which are equipped with width adjustment systems, based on principles and elements of mechanical character, which require a manual intervention by the operator, and are, e.g., of the sliding-guide type, with blocking by means of screws; when it is necessary to act on the width control device inside the tubular knitted fabric, the textile finishing machine must be stopped.
It is evident that such a procedure causes time and production losses, an additional use of manpower, machine stoppage and cost increases, besides the undoubted difficulty of the intervention.
Furthermore, single machines or calenders of various types are used, which are different from each other essentially because of the usable cylinder types, as well as due to the different mechanical action they perform on the tubular knitted fabric. Thus, devices exist, which are equipped with drafting calenders, polishing calenders, friction calenders, and so forth.
The selection of the equipment to be used depends both on the type of tubular knitted fabric to be processed, e.g., determined by the different fibrous compositions and interlacing patterns of the knitted fabric, and on the finishing effect to be given, so that, according to the different cases, different calender types are used in sequence, which requires replacement of, the calender or equipment being used to be replaced.
The selection of the equipment is also a function of its installation in a processing line including downstream machines of different types, e.g., a dryer.
The case frequently occurs furthermore, in which the same article of tubular knitted fabric must be calendered with two different machines, and, hence, by two sequential passages, e.g., by first using a polishing calender equipped with a polished cylinder, and then a drafting calender, equipped with cylinders coated with a textile material.
Another problem which occurs frequently with some types of tubular knitted fabric, is in obtaining the required end width of the flattened tubular fabric by means of only one calendering passage. Namely, due to the deformations of the tubular knitted fabric during preceding wet-treatments, such as mercerization, bleaching, and/or dyeing, an excessive decrease in the original width is produced.
In such case, both the expansion and the overfeeding of the tubular knitted fabric must be performed gradually and progressively at least two sequential passages through the calendering machine.
It is evident that a double calendering passage, whatever the reasons requiring it may be, and whether it is carried out on the same calendering machine, or on two different calendering machines, causes a considerable decrease in productivity, higher than 50%, and a corresponding increase in production costs.